The present invention is directed to a hydraulic cement admixture, improved cement compositions containing said admixture and to processes of forming said admixture product. Specifically, the present invention relates to a hydraulic cement admixture product composed of certain derivatives of polyacrylic acid polymers, as fully described below, which are capable of imparting high flowability to cement compositions and of causing the treated compositions to retain high flowability over a sustained period of time without imparting a significant delay in the initial set time.
Although increased flowability can be attained by using large dosages of water in a hydrating cement composition, it is well known that the resultant cement based structure will have poor compressive strength and related properties. Various additives have been proposed to increase the flowability (known as "slump") of cement composition, such as mortar and concrete compositions, without increasing the water content of the initially formed composition. Such additives have been classified as "cement superplasticizers" and include, for example, compounds, such as naphthalene sulfonate-formaldehyde condensates lignin sulfonates and the like.
More recently, copolymers of alkenyl ethers and acrylic acid or maleic anhydride, and derivatives thereof, have been proposed as agents suitable to enhance slump [Japanese Patent Publication (Kokai) Nos 285140/88 and 163108/90]. Further, copolymers formed from the copolymerization of hydroxy-terminated allylether and maleic anhydride or the allylether and a salt, ester or amide derivative of maleic anhydride such as disclosed in U.S. Pat. No. 4,471,100 have been proposed as cement admixtures capable of enhancing slump.
In each of the above instances, the proposed cement admixture material when used in a cement composition does not provide the desired combination of properties or only provide them in low degrees. For example, esterified acrylate copolymers, while providing good slump enhancement, also causes the treated cement composition to exhibit excessive set retardation.
Prior acrylic acid polymer derivatives have been formed by first reacting acrylic acid with the derivative forming amine and then subjecting the vinyl amide monomer to vinyl polymerization conditions. Such polymerization is difficult to control, provides product of a wide distribution of molecular weight and does not permit desired imide moieties to be present in the resultant polymer.
It is highly desired to have an admixture which is capable of imparting to a treated cement composition, a high degree of slump, of preventing a decrease in slump (decrease in flowability) over a sustained period of time, and at the same time, not causing the composition to exhibit excessive set retardation.
It is further highly desired to provide a simple process for forming the desired polymeric admixture.